<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>土豆首页</title>
    <style>

        * {
            margin: 0;
            padding: 0;
        }

        a {
            margin: 100px;
            width: 448px;
            height: 252px;
            display: block;
            position: relative;
        }

        .mask {
            width: 100%;
            height: 100%;
            background: rgba(0, 0, 0, .4) url("../image/tudou_arr.png") no-repeat center;
            position: absolute;
            top: 0;
            left: 0;
            /*默认隐藏*/
            display: none;
        }

        /*当鼠标经过时的 mask 显示出来*/
        a:hover .mask {
            display: block;
        }


    </style>
</head>
<body>
<a href="#">
    <img src="../image/tudou.jpg">
    <div class="mask"></div>
</a>

</body>
</html>